With continuous developments of wireless communication technology, nowadays users can transmit information through wireless communication systems without geometric restrictions. An antenna is one of the important elements in wireless communication. At present the antenna made from a printed circuit board is most popular. It is easier to fabricate and costs less.
The commonly used wireless communication standards now are IEEE802.11 a and IEEE802.11b announced by the Electrical and Electronic Engineering Institute (IEEE). IEEE802.11a is for the band of 5 GHz. IEEE802.11b is for the band of 2.4 GHz. Design of the antenna baseboard has to comply with the corresponding bandwidth. If a wireless communication system has to be used in two different bands at the same time, matching antennas have to be provided. This causes inconvenience. To meet the requirement of different bands, adopting a bi-frequency antenna design is a growing trend. However, the present bi-frequency antenna still has drawbacks, such as an insufficient bandwidth and integration difficulties.
Hence how to provide a broadband bi-frequency antenna is one of the research and development focuses in the industry.